Evaluation of Anti-inflammatory and Antinociceptive Potentials of Khaya senegalensis A. Juss (Meliaceae) Stem Bark Aqueous Extract

Aim: To investigate anti-inflammatory and antinociceptive potentials of aqueous stem bark extract of Khaya senegalensis A. Juss (Meliaceae) in rodents.
Methodology: Anti-inflammatory activity of aqueous stem bark extract of K. senegalensis (AKS) was studied in different models. Effect of the extract in acute inflammation was tested in carrageenan-induced rat paw edema and its effect in chronic inflammation was evaluated using cotton pellet-induced granuloma test. Croton oil-induced ear edema in mice was used to investigate the effect of the extract on topical inflammation. Antinociceptive property of AKS was evaluated using three models of nociception: hot-plate test, acetic acid-induced writhing in mice and formalin-induced paw licking in rats. Membrane stabilizing effect of AKS was tested in heat and hypotonicity-induced hemolysis. The mechanism of antinociceptive effect of the extract was evaluated by pre-treating rats with metoclopramide, a dopamine (D2) antagonist (1.5 mg/kg body wt.) and naloxone, an opioid receptor antagonist (5 mg/kg body wt.). One hour after these treatments, the rats were given AKS (150 mg/kg p.o) and their reaction time in hot-plate was assessed. Free-radical scavenging activity of the extract was measured by decrease in the absorbance of 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) methanol solution.
Results: The extract produced significant (P<0.05) and dose-dependent inhibition of ear edema in mice. It also caused a significant (P<0.05) reduction in granuloma formation and paw edema in rats. At concentration range of 125 - 500 µg/ml, AKS significantly (P<0.05) protects the erythrocyte membrane against lysis induced by heat and hypotonic medium. It also significantly (P<0.05) reduced the licking/biting time of the formalin-injected rat paw in the early (19 - 51 % reduction) and late (13 - 57 % reduction) phases. The extract demonstrated significant (P<0.05) antinociceptive activity in the hot-plate and writhing tests and exhibited good scavenging effect on DPPH free radical.
Conclusion: The study demonstrated that Khaya senegalensis stem bark aqueous extract possesses anti-inflammatory activity and antinociceptive effect mediated via central and peripheral mechanisms. Further studies on the plant may produce lead molecules for the development of new anti-inflammatory drugs.